Manufacture of cellulosic fluffed sheet

ABSTRACT

A METHOD FOR PRODUCTION OF AN ABSORBENT, SOFT, LIMP CELLULOSIC FIBROUS BODY HAVING LAYERS OF DIFFERENTIAL ABSORPTION CHARACTERISTICS IN WHICH A WET CELLULOSIC BATT WITH A MOISTURE CONTENT OF AT LEAST 30% IS TREATED WITH A DILUTE AQUEOUS SOLUTION OF CELLULOSIC DEBONDING AGENT SUCH AS A QUATERNARY AMMONIUM SALT SO AS TO PENETRATE ONLY A SURFACE ZONE OF THE BATT AND TO LESSEN TO COHERENCE OF THE FIBERS FOR EACH OTHER IN THIS ZONE. THE BATT IS DRIED TO A CONSISTENCY OF AT LEAST 85% IN THE ABSENCE OF SUBSTANTIAL POSITIVE PRESSURE, AND THEN TO FURTHER OPEN THE FIBERS IN THE SURFACE ZONE. THE BATT IS FLEXED ABOUT AN AXIS TRANSVERSE TO ITS LENGTH AND SUBJECTED TO A STREAM OF NONREACTIVE GAS. THE BATT INTEGRITY IS MAINTAINED THROUGHOUT THE PROCESS, WITH THE RESULTING BODY HAVING A DENSE ABSORBENT INNER ZONE AND A SOFTER MORE FLUID PERIOUS OUTER ZONE.

1971 J. F. cH-AMPAIGNE 1 3,

MANUFACTURE OF CELLULOSIC FLUFFED SHEET Filed April 22, 1968 2 Sheets-Sheet 1 PmmIm QJDQ mo AOOU 1. 19; .1971 CHAMPAIGNE 3,556,931

' MANUFACTURE OF' CELLULOSIC FLUFFED SHEET Filed 5 1-11 22. 1968 z S heets-Sheet a United States Patent 0 berly-Clark Corporation, Neenah, Wis., a corporation of Delaware Filed Apr. 22, 1968, Ser. No. 726,642

Int. Cl. D2141 3/00 US. Cl. 162-158 7 Claims ABSTRACT OF THE DISCLOSURE A method for production of an absorbent, soft, limp cellulosic fibrous body having layers of differential ab; sorption characteristics in which a wet cellulosic batt with a moisture content of. at least 30% is treated with a dilute aqueous solution of cellulosic debonding agent such as a quaternary ammonium salt so as to penetrate only a surface zone of the batt and to lessen the coherence of the fibers for each other in this zone. The batt is dried to a consistency of at least 85% in the absence of substantial positive pressure, and then to further open the fibers in the surface zone, the batt is flexed about an axis transverse to its length and subjected to a stream of nonreactive gas. The batt integrity is maintained throughout the process, with the resulting body having a dense absorbent inner zone and a softer more fluid pervious outer zone.

BACKGROUND OF THE INVENTION Field of the invention The invention with relation to the prior art ,Cellulosic fluff batts are commonly produced by mechanically defiberizing dried pulpboard sheets and air forming the resulting fibers. For many purposes the pulpboard is well adapted for conversion into fluff and, addi-.

tionally; it is of low cost and readily handleable. The mechanical action involved in defiberizing, however, tends to cause the fluff batts to be dusty and, unless embossed or enclosed, the fluff tends to be excessively dusty, that is, to contain an undesirable quantity of fines.

' In the practice of this invention I form an absorbent cellulosic batt having one or both opposed surface zones of excellent softness characteristics; further, the surface zones have less tendency to become and remain wetted and, therefore, the product is quite useful in the formation of articles which contact the skin, that is, in bandages, sanitary napkins and the like. lmportantly, although the bulk and openness ofthe surface zone or zones is comparatively large, the overall capacity for fluid retention of a product formed from the fluff sheet is excellent. This is due to the relatively dense, small pored zone or layer of compacted fibers adjacent the surface zone, this more dense layer serving to retain large quantities of fluid.

I form my sheet of differential absorption characteristics by a series of basic procedural steps involving (a) the treating of a wet (at least 30% by weight of moisture on the bone dry fiber weight) cellulosic pulp batt with a dilute aqueous solution of a fiber debonding or softening agent to penetrate a surface zone of the web and decrease the coherence of fibers in the surface zone without significant entry of the agent to the main fiber body;

(b) drying the batt in the absence of positive pressure on the batt to expel moisture from the batt interior through a surface zone or zones-the withdrawing of moisture from the compacted fibers of the interior causes bonding of such fibers into the customary relatively dense sheet while the moisture passing outwardly of the sheet tends to further interrupt the debonding of fibers of a surface zone as initiated by the debonding agent; (c) mechanically working, by flexing or the like, in the absence of any significant abrasion the dry web so that fiber bonds formed in the surface zones tend to be broken and opened while the interior fiber bonds close to the neutral axis of the sheet are little affected; ((1) supporting the opened batt between foraminous members rather tightly while directing an air blast or blasts to the sheet to fluff the relatively unbonded fibers; the air blasts make no significant penetration of the sheet core and, accordingly, opposed blasts are directed to the opposite sides of a sheet for effecting the flufiing of opposite sheet sides.

The product may be softened on one side only and the soft surface zone is then backed by a relatively dense fluff zone; more commonly, both opposed surfaces are softened and the dense zone is a core of relatively compacted fibers, the core having small pores or capillaries which tend to draw fluid from the surface zones tending to maintain the latter relatively dry in use.

In a preferred embodiment of the process, as set out in detail hereinafter, the pulp after bleaching and washing, is formed without drying into a loose wet batt and then is subsequently subjected to the debonding agent application. Alternatively, the dried pulp sheet received from a pulp mill may be reslurried by conventional means, formed into a loose wet batt and processed in accordance with the invention but less economically than in the preceding method. Also, the dried pulp sheet may be first well wetted with water and then subjected to the bonding agent without reslurrying, followed by the noted drying, fiuifing and gas blast steps; while this procedure avoids reslurrying, the former procedures are favored to achieve a more soft and more limp product.

The debonding agent treatment is most suitably by spray application just before the traveling sheet is passed to the drying stage; this permits application to opposite sides of the sheet simultaneously. However, the agent may be applied by other means such as an aspirator, print roll or other roll applicator means, a pattern of the agent rather than a continuous application being very suitable for control of quantity.

The density of the product in the more dense zone is about that of the density of the dried pulp sheet as received from the pulp mill or is about the density of the reslurried bleached pulp sheet; in either event the density in the more dense zone is about 1 to about 4 times that of the density of the pulp in a surface zone. Further, the more dense zone supplies strength to the product since the fiber bonds in this area are largely unaffected by the mechanical and wetting actions; additionally, since the product is integral in the sense that it is composed of one formed sheet, some fibers of the surface zones will be entwined with and retained by fibers of the more compact zone providing against easy delamination and the like even under severe wetting conditions of use.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

FIG. 1 is a view illustrating a typical equipment arrangement for the formation of a cellulosic fluff sheet in accordance with a preferred embodiment of the invention;

FIG. 2 is a view of a product in accordance with the invention; and

FIG. 3 is a view of a product like that of FIG. 2 but with a surface zone drawn back to illustrate the relative bulks in a typical product.

Referring now to the drawings, the numeral 1 in FIG. 1 designates a source of slurried bleached kraft pulp. The

slurried bleached kraft is fed through line 2 to a formingmachine designated at 3; the latter includes a reservoir 4 and a screen cylinder 5. Wiper 6 serves to remove pulp from the screen cylinder and to maintain the cylinder clean as pulp sheet 7 passes to the Wet presses generally indicated at 8 and 9. The pulp as it is formed on the cylinder machine is relatively open, and the wet presses" serve primarily to remove water but also to condense to I 1 formed into a sheet of uniform density andof a ,weight of some extent the traveling sheet. Sheet 7 is then presented to a series of heated rolls designated at 10, 11 which are efiective to raise the temperature of the sheet to about 120 F. The moisture content, based on the dry fiber weight, at this time is aproximatley 60%. From the heated rolls the sheet 7 is directed to a final wet pressing between calender rolls 12. From the calender rolls the sheet, at a moisture content of approximately 50%, is presented over guide rolls 13 to spray mechanism designated at 14, 15. Spray 14 applies an aqueous solution of a 'debonding agent at a concentration of about 2% to the upper side of the sheet. Spray 15 applies a similar solu-- No external pressure is applied during water removal as such would tend to cause fiber bonding. As the water in the form of steam passes outwardly from the central zone of the sheet, it further interrupts the bonds in the outer surface zones thus aiding the debonding agent in its function. The sheet is Well dried at 16 to a consistency of 85% and preferably 95%. At this time the interior of the sheet is well dried and well bonded and comprises pulp fibers defining small capillaries or pores, the pulp fibers of this interior zone lying primarily on the neutral axis of the sheet. The debonding agent in the surface zones inhibits bonding of the fibers in these zones, however, and

the sheet is, therefore, more open at the surface.

The dry sheet is next subjected to a series of flexing actions by being passed over rolls 17, 18', 19, 20, 21 and 22 in sequence; the reverse bending of the sheet breaks particularly bonds in the outer zones since the latter are well off the neutral axis. The surface zones now consist primarily of fibers which are very loosely bonded to each other; the sheet is then passed over guide roll 27 between opposed endless belt screens 23, 24 and is retained tightly therebetween. A degree of tightness is required to aid in retention of surface fibers as they are commonly so little bonded that a very large quantity would be lost in the air blast. The wires of the traveling screens 23, 24 are well spaced, the wires having a mesh of about 18 x 14.'

Within the strands of the screens there are positioned air jets 25 and 26 for directing air to the confined pulp sheet from opposite sides. The air blasts are at a relatively high pressure of about 40 to about 85 pounds per square inch and serve to further disrupt those bonds which may survive the flexing action.

The sheet, when formed as described, is in continuous lengths and may be directed to windup or converted into finished products as desired.

As illustrated in FIG. 2, the sheet, in accordance with the invention, includes a relatively compact interior zone 29 of fibers bounded on each side by relatively open surface zones 30, 31. The outer surface zones, when the product is formed in accordance with the above description, commonly have a density which is /3 to A that of the adjacent interior zone 29: 'Fu'rtherfsiiieetheprdd uct is formed of a single sheet and the fibers intermingle to some extent, some fibers will project from the outer zones to the interior, and fibers of the interior will project into the outer zones; such are indicated, at. 32 and 33 in FIG. 3 and serve to inhibit against product delamination in use. It will be appreciated, howeventhat the primary strength of the productlies in the compacted fiber zone where fiber bonding is good and similar toathatnofithe bonding of the original pulp sheet. It will'further be noted that the necessity forand expense of adhesive for retention of plies, for example, is eliminated."

Further, by way of specific application, kraft pulp is about 275 pounds per 3000 sq. ft. at ani'oisture content of about 50%.- This sheet is-subje'cted to sprays as 14,

1 5 .in FIG. 1 .of a 2% aqueous solution of di-stea'ryl dimethyl ammonium chloride, a:commercially"available;

softener, then dried to a moisture content of about 95%- and ,fiexed over pulleys of a diameter. of about 6.The

sheet, when subjected to an-air' blast. of about lO Oundspcr. sq. in. on, each side, hasa density in'zone29 of about 0.18 gram per cc. and a-density.in zones 30,31 of about condensates are also useful. The base sheet material may be any conventional pulp; kraft is preferred but sulfite and, to some extent,

0.06 gram per cc. The surfaceis soft feeling, absorbent and, when wetted lightly, quite readily passes the fluid: to the interior, retaininga dry surface touch. I

. Formation of the sheet as described herein has been with reference to a cylinder machine. It Will be appreciated-- that other equipment, particularly the usual Fourdrinier' machine, may besimilarly employed. 1 I

Also, while I prefer to employ as debonding or softening agents cationics such as quaternary ammonium salts containing stearyl groups and polymeric surface active quaternary ammonium salts as described in US. Pat. No. 2,454,547, other softening agents, alone or in combination with the quaternaries, such as glycerine and lanolin,

are useful. Generally, an aqueoussolution of 1 /2 3 concentration of the softener by weight is effective to provide a 0.75% to 1.5% pickup on a dry. fiber basis of the softener, and such is effective for my purpose. The com mercially avilable softening agents marketed under the" trademark Arquad by Armour and Company and under stood to be quaternary ammonium salts of alkyl trimethyl ammonium chloride where the alkyl. chain is composed of aliphatic chains ranging from 8 to18 carbon atoms serve the purpose well. 0ther known agents such as" or ethylene oxide ester the ethoxylated dodecyl phenol groundwood or semi-chemical pulps, may be included in the furnish. The sheet must have sufiicie'nt strength to permit it to "be carried through the various operations and this will vary somewhat the sheet furnish; however, 60

% moisture at the sprays is usually about the maximum):

.The thickness'of the layers of the outer zones 30,

in FIG. 2 may be about that of the center or" interior more dense zone; this is controllable -to some extent controlling the depth of penetration of 'the softening determinable by simple experimentation.

As'many apparently widely different embodiments 'or this invention may be made without departingfrom the" spirit and scope thereof, it is to be under-stood that Ido' not limit myself to the specific embodiments thereof ex cept as defined in the appended claims.

I claim:

1. A method of producing an absorbent, soft, limp cellulosic fibrous body having layers of differential absorption characteristics for fluids, said method comprising surface treating a wet cellulosic pulp batt having at least 30% moisture by weight based on the bone dry fiber weight with a dilute aqueous solution of a cellulosic fiber debonding agent to penetrate only a surface zone of the batt and to decrease the coherence of fibers for each other in the surface zone of the batt while leaving the coherence of fibers for each other in the interior of the batt substantially unaffected, drying the batt to a consistency of at least about 85% in the absence of sub stantial positive pressure on the surface zone so that the fibers of the surface zone are largely uncompacted, flexing the batt of said consistency by bending it about an axis transverse to the length of the batt to further open the batt in the surface zone, supporting the opened batt firmly between moving foraminous member means and impinging a gas stream nonreactive to the fibers to the supported batt to further disrupt bonds in the surface zone of the batt and to further dry the fibers of the surface zone.

2. A method according to claim 1 in which the Wet cellulosic pulp batt subjected to the dilute aqueous solution of debonding agent is a batt of never dried fibers.

3. A method according to claim -1 in which the wet cellulosic pulp batt is of a bleached pulp.

4. A method according to claim 1 in which opposite sides of the opened batt are subjected simultaneously to gas blasts while the batt is retained between the foraminous member means.

5. A method according to claim 1 in which the wet cellulosic pulp batt is surface treated with a solution of a debonding agent having a debonding agent concentration of between about 1 /2 to about 3%.

6. A method according to claim 1 in which the aque- Ous solution of debonding agent is applied in a pattern.

7. A method of producing an absorbent, soft, limp cellulosic fibrous body by the conversion of a cellulosic pulp batt, which method comprises longitudinally advancing a wet cellulosic pulp batt through Wet pressing and heating means to provide the cellulosic batt with a moisture content of between about 30% and spraying a dilute aqueous solution of a debonding agent for cellulosic fibers to the batt surface zone to further Wet the batt surface relative to the batt interior, drying the advancing batt to a consistency of at least about so that the fiber interior has a greater moisture percentage than the batt surface zone, said drying serving to debond the fibers in the surface zone relative to the fibers of the batt interior, flexing the batt at said consistency about an axis transverse to the length of the batt to further debond the fibers of the surface zone, and while maintaining batt integrity blasting the fibers of the surface zone with air to fluff the fibers of the surface zone.

US. Cl. X.R. 

